A liquid crystal display (LCD) has broadened their applications as our society has changed to an information society and the technology has developed. In recent years, there have been increasing demands for LCDs with light weight, slim design, and low electrical power consumption.
Recently, a light emitting diode (LED) is mainly used for a light source of a backlight unit (BLU) owing to its high brightness and long life span. For an edge-lit backlight unit, however, a fewer number of LEDs are employed in order to resolve the problems of high cost and heat release. Further, a dual brightness enhancement film (DBEF) sheet tends not to be employed as a reflective polarization film above a prism for reducing the manufacturing cost.
As a result, there has been a demand for a high performance optical sheet having improved brightness suitable for use as an optical film as well as high diffusivity for hiding the pattern of a prism sheet.
Korean Laid-open Patent Publication No. 2010-0042310 discloses a light diffusion film with high quality luminance, which has enhanced brightness by adjusting the shape and rate of protrusions of a hemisphere lens. However, the light diffusion film has possible risks of interfacial scratch as well as surface stain defects due to vibration friction of the protrusions when they are in contact with a polarizing plate.
Further, Japanese Laid-open Patent Publication No. 2000-193805 discloses a light diffusive sheet, which provides uniform light diffusion although it does not employ spherical beads. The light diffusion sheet, however, has unsatisfactory optical properties in terms of brightness, hiding power, viewing angle, and the like.
Thus, there is a need to provide a method for manufacturing an optical sheet that can resolve the aforementioned problems.